This invention relates to hydrostatic transmissions in general and in particular to such transmissions used in applications known as zero turn (xe2x80x9cZTxe2x80x9d) vehicles, where the transmission has two independent outputs that can drive the vehicle wheels in opposite directions.
One known ZT design incorporates two separate hydrostatic transmissions and two separate gear and axle housings; with each transmission bolted to a separate housing. A design of this type is shown in U.S. Pat. No. 5,078,222. While such designs offer flexibility, the use of two separate HSTs increases the costs and complexity of the unit.
Other known designs incorporate the hydrostatic transmission and the two output axles into a single housing. Such designs lack the necessary flexibility required to adapt the transaxle unit to a variety of vehicle applications.
The present invention teaches a zero turn transaxle that solves the aforementioned problems by presenting a low cost yet flexible design. The preferred embodiment of this design uses a transmission housing in which a pair of hydraulic pumps and a pair of hydraulic motors are mounted on a porting block, in which the hydraulic porting to connect the respective pumps and motors is formed. The transmission includes a pair of motor output shafts engaged to and driven by the respective motors; these output shafts extend outside the transmission housing.
A pair of separate axle housings are mounted on opposite sides of the transmission housing and include various gears and output axles. The use of the separate axle housings permits the user a wide degree of flexibility in how the unit is assembled, so that it may fit into different types of ZT vehicles and may be used for a variety of industrial applications. Such flexibility includes the ability to orient the axle drive units in various positions with respect to the transmission, including having orientations of the axle drive units that would permit the axle shafts to be non-coaxial. The transmission housing is configured so that with a particular orientation of the axle drive units the transmission may be positioned such that the input shaft may be on the right or left side of the transaxle centerline. Variations in vehicle frame width may be accommodated by either moving the location of the mounting interface on the axle drive unit housings, or replacing the housing with the axle horn with one that has a different axle horn length, while leaving all other components identical to the basic configuration.
Other benefits and objects of this invention are disclosed herein and will be obvious to readers of ordinary skill in the art. The features disclosed herein can be combined to create a unique hydrostatic transmission design; it is understood, however, that such features are unique in their own right and can be used independently with other transmission designs, as will be obvious to one of ordinary skill in the art.